Filaments for cutting vegetation are generally made by extrusion of a thermoplastic material, including polyamide in particular, and having a variety of shapes.
While the oldest filaments had a circular cross-section and were smooth throughout, filaments having a variety of cross-sections have been developed in order to improve cutting quality (presence of edges, etc.) and/or the lifetime of the filament, and/or to reduce the operating noise of the machine by operating on turbulence.
Thus there are filaments comprising ridges, grooves, slots, or even local distortions of the filament along its length.
For the sake of saving space, cutting filaments are generally sold as coils.
However, the stiffness of the materials of which they are constituted implies that they cannot remain coiled and that the coil therefore unwinds if it is not held by some means of retention.
Typically, cutting filament coils are sold in packaging having shape and dimensions matching the shape and dimensions of the coil, so that its shape is maintained by the inner walls of the box.
To use the filament in a cutting machine, it is necessary to reel off a certain length of filament and to wind it around the hub of the cutting head, allowing a portion needed for cutting to emerge from a side opening of the cutting head.
This operation consisting of placing the filament in the cutting head is a tedious operation.
Further, due to its stiffness, the filament has a tendency to unwind even after it is in place in the cutting head, making it difficult to control the length which emerges from the head for performing the cutting.
To correct these drawbacks, coils that are self-supporting, that is to say consisting of turns bonded to one another but separable by a pulling force exerted on the free end of the filament, have been proposed.
Thus, document U.S. Pat. No. 4,024,635 proposes a self-supporting coil, the different turns whereof are bonded to one another by welding, by an adhesive or by injection of breakable connections between two adjoining turns.
Document FR 2 967 548 proposes, for its part, a filament having reciprocal retention provisions such that, when the filament is wound upon itself, each turn cooperates with at least one adjoining turn so as to retain it mechanically.
This filament therefore makes it possible in particular to make a self-supporting coil in the form of a disk for example.
To use the self-supporting coil directly in a cutting machine, that is without having to reel off the coil and then wind the filament onto the hub of the cutting head as is necessary with conventional coils, document U.S. Pat. No. 4,024,635 cited earlier proposes a cutting head wherein the self-supporting coil is captured between an upper portion designed to be attached to the device driving the machine in rotation and a lower portion removably fixed to the upper part by a central nut.
The coil is centered relative to the head by its central void, which is accommodated by a revolving cylindrical stud built into the upper portion of the cutting head, and gripped between the upper and lower portions of the head in such a position that the free end of the filament extends through an opening provided in said upper portion for a length predetermined for performing the cutting.
When the filament is worn out, the used portion is cut off and a new portion of filament is paid out.
To this end, it is necessary to loosen the central nut to spread slightly the upper portion and the lower portion of the cutting head, then a pull is exerted on the filament to reel off a portion of it.
The central nut is then re-tightened to ensure that the coil is held between the upper portion and the lower portion of the cutting head.
Though having a simple design, this cutting head has the disadvantage of requiring partial loosening of the lower and upper portions of the cutting head each time a new length of filament must be made available.
Further, this head only allows manual payout of the filament, which requires completely stopping the machine.
A certain number of cutting heads on the market, however, are provided with a “tap and go” system which makes it possible, after a simple tap against the ground by the lower portion of the cutting head, to automatically reel off a predetermined length of filament, while the machine is operating.
Due to its design which captures the coil between the lower and upper portions, the cutting head described above is not compatible with such a system.
One goal of the invention is therefore to design a cutting head which allows a self-supporting coil to be used directly, that is without involving cutting filament reeling off and rewinding operations, and wherein the extraction of a length of filament is simplified.
Preferably, the design of said cutting head should be compatible with the automatic “tap and go” payout system mentioned above.
Another goal of the invention is to propose a cutting assembly having a cutting head and a self-supporting coil specifically matched to one another.